Satellite networking systems supporting two-way communications that have one active ground station functioning as the master station and a plurality of widely distributed slave stations are very common today. These slave stations are often called “VSATs”—Very Small Aperture Terminals—or simply “terminals.” There are international standards defining how such VSAT networks should be built and operated. The most comprehensive and widely adopted standard is the DVB-RCS standard which is a family of DVB (Direct Video Broadcast) standards developed by the DVB Project and published by the European Technical Standards Institute (ETSI). See ETSI EN 301 790 and www.etsi.org.
The DVB-RCS standard utilizes TDM (Time Division Multiplexing) on the forward channel to the VSATs, and MF-TDMA (Multi-Frequency Time Division Multiple Access) techniques on the return channels to the master station. Most such VSAT networks today—even those not based on the DVB-RCS standard—use TDM and MF-TDMA techniques in a similar way as described in the DVB-RCS standard, though particular details of their implementations may differ. Some older technology VSAT networks may still use a single return channel (at a single carrier frequency) and, therefore, only employ TDMA.
The embodiments disclosed herein apply to any type of VSAT network that utilizes TDM communications from the master station and either MF-TDMA or simply TDMA techniques on the return channel communications to the master station in what forms a star topology network with the master at the hub. They also apply to situations where slave stations or VSATs may be able to communicate to each other directly by using TDMA communications on one or more assigned channels, in what forms a mesh topology network among the slave stations, which is overlaid on a star-topology network. Both situations are common today. However, these embodiments are mere examples and do not limit the invention to these specific communication types.
VSAT networks are used for providing two-way data, voice, and/or video communication between one major location, such as near a metropolitan area or an Internet backbone site, and a variety of more remote locations, such as small businesses or homes in suburban or rural areas or entire villages or towns in remote areas of some countries. Such networks are particularly useful in areas where the terrestrial telecommunication infrastructures are less developed than those commonly found in major cities of well developed countries. They are also useful as a low-cost competitive alternative to many terrestrial services.
Today, because all VSAT network technologies only allow one active master station, their flexibility is limited. The master station usually also functions as the “gateway” between the VSAT slave stations, which are often isolated, and the rest of world's telecommunications infrastructure. (A master station or a gateway station sometimes is also called a “hub station” because of its role as the hub of a star topology network.) Therefore, a desired enhancement to VSAT networking technology of all types is to allow communication with multiple gateways with any VSAT station of the network. Such multi-gateway enhancement has applications and advantages of the following general nature:                a.) A data communication VSAT network, using the Internet Protocol (IP) or other data protocols, can direct traffic targeted for a first data processing center to a first gateway and traffic targeted for a second data processing center to a second gateway.        b.) A voice communication VSAT network, such as Voice over IP or via other means, can direct all calls within the country to a first gateway and all calls to international destinations to a second gateway.        c.) In case of the failure or destruction of a first gateway station a second gateway in the network, distant from the first, can (dynamically, automatically, and/or based on a pre-defined routing procedure, etc.) may be able to take over the role of master and provide additional reliability not available in current VSAT networks.        
However, special considerations are required to enable the slave station (VSAT) to receive TDM transmission from multiple gateways and to send TDMA transmission to multiple distinct gateways. That is because the gateway station—as noted earlier—also acts as the master station for the entire VSAT network and it is not possible for a VSAT network to have two or more master stations operating concurrently.